Unfortunately, it looks like you may have destroyed your Ubuntu root filesystem while using the AOMEI Partition Assistant. Perhaps it could not identify Linux partitions, and showed them as unknown/empty partitions with no drive letter.
The fact that the Debian-style mini
grub.cfg on the ESP says the prefix setting was
/boot was not a separate filesystem; if it was, the prefix would have been set to
Before the partition modification, at this point GRUB would have been able to find a filesystem with the UUID specified in the mini
grub.cfg file. Since it cannot be found now, I'm afraid that filesystem may been overwritten or otherwise corrupted.
Your existing partitions seem to be:
(hd0,gpt1) - this is the EFI System Partition that is used to load GRUB from.
(hd0,gpt2) - by the size (only 16M), this seems to be the "Microsoft reserved" partition that is normally generated by Windows 10.
(hd0,gpt3) - size approximately 67 GB / 64 GiB, your Windows C: drive according to your comments
(hd0,gpt4) - size approximately 200GB / 191 GiB, your Windows D: drive according to your comments
(hd0,gpt5) - size approximately 870M, contents unknown. Maybe a Windows recovery partition?
According to the partition sizes and start locations, there is a gap of about 220 GiB in between
(hd0,gpt4). This is probably where the Linux partition used to be located.
So the Linux partition seems to be lost. You should find yourself a Linux Live CD (or other suitable boot media) that contains a partition recovery utility like
testdisk, and see if the Linux partition or any parts of it can be recovered.
Here's a link to a list of Live CDs that contain
You should be able to get into Windows by typing this into the GRUB prompt:
But if you need to rescue any files from the Linux partition, you should not do that right now. In fact, you should avoid any operations that might write to the disk until you've either successfully rescued all the important files from the lost Linux partition, or are satisfied that further rescue attempts will not be worth the effort.
If you want to give up trying to recover Linux, going to BIOS settings and moving "Windows Boot Manager" to the first place in the boot order should also persistently restore the ability to boot Windows (only).
You should use another computer to prepare a bootable Live CD (or other live boot media, such as a pendrive) with
testdisk or some other rescue utility available.
If you are familiar with Ubuntu, you could use Ubuntu Live functionality - you might prepare a Ubuntu installation USB and use its "Try Ubuntu" functionality, and then just use the usual package management tools to automatically download & install
testdisk to a RAM-based installation. In this case, you'll need to do that again each time you boot from the USB in order to have the tool available.
Or you might use a longer procedure to set up a live USB with persistence or make a complete USB-based installation of Ubuntu; both of these options should allow you to use the standard package management tools to add
testdisk and/or other recovery tools to the USB before coming back to the computer with the damaged Linux partition, booting it from the pendrive and making a recovery attempt.
You'll also need a second pendrive or other media you can use to save any recovered files into; although you might be able to mount the Windows D: drive and use it to store the recovered files, as it seems to be not overlapping the missing partition.
Once you can boot the computer from a pendrive and run
testdisk on the computer's HDD (e.g. just
sudo testdisk /dev/sda or whatever the device name of the HDD ends up being), the next steps depend on what it will report. In the best case, it might be able to simply undo what AOMEI did and restore the missing partition.
AOMEI Partition Assistant seems to be aimed for Windows users only, as it does not seem to support any non-Windows partition types. In the future, you may wish to use
gparted instead for modifying the partitioning of any computer that has Linux installed.